1. Field of the Invention
The invention relates to a double-balanced mixer and, in particular, to a double-balance mixer with a dynamic current steering cell.
2. Description of the Related Art
Mixer circuits for high frequency applications constructed using metal oxide semiconductor (MOS) transistors are subject to a limited voltage supply (usually less than 2V) and high levels of flicker noise, having frequencies extending to several tens of MHz. Accordingly, the gain and output signal level required in such mixer circuits exceed those required in the equivalent bipolar circuits.
FIG. 1 is a circuit diagram illustrating a conventional double balanced mixer circuit. The double balanced mixer circuit in FIG. 1 includes differential pairs of MOSFETs (Q131-Q132 and Q133-Q134). The drains of the pairs of MOSFETs are connected to an output terminal (Output-I+ and Output-I−). The gates of the pairs of MOSFETs are connected to first input terminals (Input-II+ and Input-II−). The double balanced mixer circuit in FIG. 1 also includes active devices Q135, Q136, Q137 and Q138. The sources of the MOSFET pair Q131-Q132 are connected to the drains of the active devices Q135 and Q136. The sources of the MOSFET pair Q133-Q134 are connected to the drains of the active devices Q137 and Q138. The gates of the active devices Q135, Q136, Q137 and Q138 are connected to the second input terminal (Input-I+ and Input-I−). The sources of the active devices Q135, Q136, Q137 and Q138 are connected to the ground through an impedance unit (Degeneration Impedance).
FIG. 2 is a circuit diagram of a conventional quadrature mixer disclosed by Raj a S Pullela et. al in ISSCC 2006. The conventional quadrature mixer 200 comprises an I-Mixer Quad 210, a Q-Mixer Quad 220, a 2x LO stage 230, and a transconductor stage 240. The I-Mixer Quad 210 in FIG. 2 includes differential pairs of MOSFETs (M9-M10 and M11-M12). The drains of the pairs of MOSFETs are connected to an output terminal (BBIp and BBIn). The gates of the pairs of MOSFETs are connected to first input terminals (LOIp and LOIn). The Q-Mixer Quad 220 in FIG. 2 includes differential pairs of MOSFETs (M13-M14 and M15-M16). The drains of the pairs of MOSFETs are connected to an output terminal (BBQp and BBQn). The gates of the pairs of MOSFETs are connected to first input terminals (LOQp and LOQn). The 2x LO stage 230 comprises MOSFETs M5, M6, M7 and M8. Sources of the MOSFETs M9-M10 and M11-M12 are respectively connected to drains of the MOSFETs M5 and M7 and those of the MOSFETs M13-M14 and M15-M16 respectively connected to drains of the MOSFETs M6 and M8. Gates of the MOSFETs M5 and M7 are connected to an input terminal 2Lop and those of the MOSFETs M6 and M8 connected to an input terminal 2Lon. MOSFETs M1 and M3 are connected between the sources of the MOSFETs M5-M6 and a ground GND and MOSFETs M2 and M4 connected between the sources of the MOSFETs M7-M8 and the ground. Gates of the MOSFETs M1 and M3 are connected to an input terminal RF+ and those of the MOSFETs M2 and M4 connected to an input terminal RF−.